add vendoring with go dep

vendor/golang.org/x/net/icmp/sys_freebsd.go

@@ -0,0 +1,11 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package icmp
+
+import "syscall"
+
+func init() {
+	freebsdVersion, _ = syscall.SysctlUint32("kern.osreldate")
+}